1. Field of the Invention
The present invention relates to a wireless system to be mounted on a vehicle, and more particularly, to an in-vehicle wireless system that receives and copies high-frequency wireless signals from transmitters that remotely control garage door opening-closing mechanisms, household equipments, and the likes, and transmits high-frequency wireless signals for operating the garage door opening-closing mechanisms and the likes.
2. Description of the Related Art
As remote controllers for controlling various household electric equipments and devices from a distance have widely spread, universal remote controllers that can remotely control devices and equipments with a single controller are now used in some places. Since infrared rays are used for remotely controlling most household electric equipments, a typical universal remote controller is designed to receive and copy an optical signal transmitted from the remote controller of an equipment or the like, and transmit an optical signal based on the copy to a selected equipment or the like when controlling the equipment.
Likewise, remote controllers for controlling garage door opening-closing mechanisms and the like have widely spread, and each remote controller is specially designed for each corresponding mechanism. However, having more than one remote controller and operating the remote controllers separately from one another in a vehicle is not convenient to users. Therefore, there are some in-vehicle wireless systems that can perform remote control on two or more garage door opening-closing mechanisms and the likes with a single remote control.
While optical signals are normally used for remotely controlling household electric equipments and the likes, wireless high-frequency signals are mainly used for remotely controlling garage door opening-closing mechanisms and the likes. This is because the control operation needs to be made possible even if the receiver of the target mechanism cannot be seen from the transmitter in the vehicle.
In most remote control operations with the use of optical signals, infrared rays of 940 nm in wavelength are modulated by frequencies in the neighborhood of 40 kHz, and PPM (Pulse Position Modulation) control codes are transmitted. Accordingly, the universal remote controllers should copy the switching on and off of the optical signals (for example, refer to Related Art 1).
On the other hand, most wireless signals used in garage door opening-closing mechanisms and the likes are high-frequency signals in a UHF band, but the carrier frequencies of high-frequency signals greatly vary among the manufacturers and product lines of the equipments. Therefore, an in-vehicle wireless system that can use for various types of garage door opening-closing mechanism and the likes need to copy the carrier frequency unique to each of the garage door opening-closing mechanisms and the likes, and the control codes contained in the high-frequency signals (for example, refer to Related Arts 2 to 14).
Conventional transmitters and receivers used in remote control operations garage door opening-closing mechanisms and the likes have simple structures for reductions in size and price. Such as, the transmitter including an oscillation circuit and an antenna that share a loop coil, the receiver of the superheterodyne type including a simple resonant circuit, or the like. In cases where such transmitters and receivers are used, the accuracy and stability of the frequencies are poorer, and the performances are degraded due to environmental changes such as temperature changes and deterioration caused with time. In some cases, there is the problem of a decrease in the distance over which transmission can be performed between a transmitter and a receiver.    [Related Art 1] U.S. Pat. No. 4,771,283    [Related Art 2] Japanese Laid-open Patent Publication No. H07-290952,    [Related Art 3] U.S. Pat. No. 5,442,340    [Related Art 4] U.S. Pat. No. 5,479,155    [Related Art 5] U.S. Pat. No. 5,583,485    [Related Art 6] U.S. Pat. No. 5,614,885    [Related Art 7] U.S. Pat. No. 5,612,981    [Related Art 8] U.S. Pat. No. 5,646,701    [Related Art 9] U.S. Pat. No. 5,661,804    [Related Art 10] U.S. Pat. No. 5,699,054    [Related Art 11] U.S. Pat. No. 5,708,415    [Related Art 12] U.S. Pat. No. 5,903,226    [Related Art 13] U.S. Pat. No. 5,854,593    [Related Art 14] U.S. Pat. No. 6,137,421
As described above, there have been in-vehicle wireless systems that can perform copying and can perform high-frequency wireless remote control on garage door opening-closing mechanisms and the likes with the use of one transmission/reception device from inside a vehicle.
In the conventional in-vehicle wireless systems that can perform copying, however, it is firstly necessary to copy both the carrier frequency of a high-frequency signal used for remotely controlling each garage door opening-closing mechanism, and a secret code contained in the signal (the control code). As a result, the high-frequency transmission circuit and reception circuit and the control method become complicated.
Secondly, the frequency characteristics and the likes of the receivers provided in garage door opening-closing mechanisms and the likes and the remote control transmitter are often unstable or frequencies of the wireless signals may be inaccurate, as described above. Also, in some cases, the transmission efficiency becomes lower due to the positions, the directionalities, and the wave polarizations of the transmission and reception antennas provided in the garage door opening-closing mechanisms, the remote control transmitter, and the in-vehicle wireless system. Furthermore, the radio waves to be received might be affected by fading, noise, or the like in some electromagnetic environment in the surrounding area. In those cases, reception becomes difficult, and the transmission distance becomes shorter.